1. FIELD OF THE INVENTION
This invention relates to a process for producing thermoplastic resins reinforced with long fibers.
In one aspect this invention is directed to a process for reinforcing resins with fibers.
In another respect, this invention relates to a process wherein fibers are first impregnated with a wetting thermoplastic polymer and then coated with another thermoplastic polymer for reinforcing.
2. DESCRIPTION OF RELATED ART
It is known in the art to reinforce thermoplastic resins with long fibers. The most classical means is to coat the strands of fiber or rovings with thermoplastic resin by extrusion. However, difficulties have been encountered which have been described and partially solved in British Pat. No. 1,094,439. These difficulties result from the poor adherence to the fibers of certain thermoplastic resins such as the polyolefins. This problem has been overcome by impregnating the fibers, before being coated with the selected thermoplastic resin, with a wetting thermoplastic polymer such as a polyolefin modified by grafting with an ethylenically unsaturated polycarboxylic acid. However, the known methods of impregnation are not quite satisfactory, the most realistic consisting in continuosly passing the fibers into a solution of wetting polymer prior to the final coating. Besides the problem of traces of solvent remaining in the material, the process is not practical and is burdensome, since it requires the handling of solvent.
In U.S. Pat. No. 3,993,726, there has been described a process for the continuous production of articles of thermoplastic resin reinforced with long fibers of glass. According to the method described, the roving is impregnated with a mixture of wetting thermoplastic resin and reinforcing thermoplastic resin in a crosshead die fed by an extruder.
The fibers are impregnated by first expanding the fibers of the roving and coating the expanded fibers in a crosshead die and passing the fibers and the thermoplastic mixture through a bar zone so that the material thoroughly penetrates into each fiber. This system is also not completely satisfactory, since the wetting polymer diluted in the other polymer loses most of its effectiveness.